I guess you have to take it to the store manager, or discuss it with whoever asked you to wait until the bill had built up to a reasonable amount.
AS for £5.00 commercials not being worth it....
a good proportion of my business is built on the back of work like this
On a Monday morning I turn out at 6am and I knock out a minimum of £220 on a variety of shops and offices and pubs in our town centre; prices ranging from £2.50 up to about £15.
I'm home by lunchtime

The only downside being that I have to go back out at 4pm to do a couple more at another village at the end of the day
These early morning shops get me out of bed at 5am every day...a bummer yes?
But it also ensures that I am out and about because I've GOT to be, ergo I am then blending my domestic work seamlessly with my commercial stuff.
Couple hours doing commercial tuesday through to friday and then on to residential.
Even a bad week is a good week now...there may be many downsides to tiny shops, but they are the backbone of my business...
Ian